Controlling the formation of quantum dot pairs using nanohole templates

 Modifying the shape of nanoholes formed by arsenic debt epitaxy by the overgrowth of a thin GaAs buffer is shown to provide a simple and robust method to grow low density lateral In(Ga)As quantum dot pairs (QDPs). We present here a systematic study of the effect of GaAs buffer thickness, InAs deposition amount, substrate temperature and arsenic overpressure on dot nucleation and QDP formation. A (10–30) nm GaAs buffer over nanoholes initially ~ 10.5 nm deep, (60–80) nm wide results in up to 80% of the nanoholes containing QDPs. The QD pairs are aligned along the [110] direction and have centre-to-centre separation of ~ 38 nm. These QDPs form following InAs deposition between 1.3 ML and 1.6 ML at 490 °C under an arsenic arrival flux of 0.6 ML/s. From the infilling of the hole prior to QD formation, we estimate a net indium surface flux towards the hole of ∼7 times the incident flux. The substrate temperature does not significantly alter the dot distribution over the range (470–510) °C. However, the QDP formation is very sensitive to the arsenic overpressure over the range (0.6–1.2) ML/s because of a partial collapse of the nanohole, due to mass transport as the substrate passes through the (2×4) to c(4×4) surface reconstruction around 500 °C.